Landing on a small body, like a comet, is particularly challenging. Even a very small impact velocity can lead to a rebound of the low gravity lander which might move the low gravity lander possibly back into deep space. Miniaturized landers cannot embark a reaction control system or a harpoon, as it was used by the low gravity lander Philae. Neither can miniaturized landers accommodate a full system of landing legs with a suspension as Philae had when landing on a comet. A simplified momentum absorption system would therefore be desirable.
Known landers have used airbags in the past. These need to be inflated at the right altitude. Hence, those landers require an altimeter. However, such altimeters are prone to malfunction. Airbags for use in space applications are also not trivial to test. For testing purposes, a vacuum chamber is required. The materials of the airbag are prone to aging and gas generators have a limited lifetime. The cost, mass and complexity are prohibitive, particularly for small landers, like low gravity landers.
Other landers have used a system of retro rockets and a sky crane lowering device. This system has a high complexity, resulting in a significant potential for contaminating a landing site.
To avoid a rebound upon landing on the landing site, the final impact velocity without having a momentum absorption device should be less than the local escape velocity. For small bodies, like low gravity landers, the velocity is in the order of several cm/s, i.e. a velocity already reached by a free fall from a small altitude. As a result, a landing device for the low gravity lander has to be deployed from a mother spacecraft extremely close to the surface of the landing site. This is inherently risky for the success of the low gravity lander or even the success of a whole mission because of the risk of the collision with the surface of the landing site.